Process for the manufacture of c-nitrosoarylamines



Patented July 17, 1951 PROCESS FOR THE MANUFACTURE OFC-NITROSOARYLAMINES Stiles M. Roberts, Easton, Pa., assignor to GeneralAniline & Film Corporation, New York, N. Y., a corporation of DelawareNo Drawing. Application December 22, 1949, Serial No. 134,596

7 Claims.

This invention relates to the manufacture of C-nitrosoarylamines bynitrosation of the corresponding secondary arylamines and rearrangementof the N-nitroso compound. More particularly, it relates to a process ofeffecting the manufacture of the C-nitrosoarylamines by a one-stepprocess directly from the corresponding secondary arylamine. Thisapplication is a continuation-in-part of my co-pending applicationSerial No. 666,532, filed May 1, 1946, now Patent No. 2,495,774.

The rearrangement of N-nitrosoarylamines to their corresponding carbonnitroso derivatives is a well-known process. It has been described asearly as 1886 by O. Fischer in connection with the preparation ofp-nitroso-N-methylaniline, pnitroso N ethylaniline, p-nitroso Nethyl-otoluidine, and 4-nitrosodiphenylamine in Berichte, volume 19,page 2994. With particular reference to the dairylamines, it has beenfound difficult to effect the rearrangement of the N- nitroso derivativeto the C-nitroso compound. It has generally been necessary to firstconvert the diarylamine to its N-nitrosoamine derivative with nitrousacid, isolate this derivative and then isomerize it by treatment withanhydrous ethyl alcoholic hydrochloric acid. The N-nitroso derivative isgenerally dried after isolation before eifecting the rearrangement.

The preparation of the C-nitrosodiarylamines, and particularly4-nitrosodiphenylamine, from the corresponding secondary diarylamines inone operation without isolation of any intermediate N-nitroso compoundis described in U. Patent 2,046,356 by Max Wyler et al. The Wylerprocess carries out the conversion under strictly anhydrous conditions.As a solvent for the diarylamine, there is employed an anhydrousalcohol, for example methyl alcohol, to which the dry hydrogen chlorideis added in an absolute alcohol solution. The required alkali metalnitrite for the conversion is added in dry powdered form. When N-alkylarylamines are used for this conversion, the same reaction can beaccomplished, and was accomplished by O. Fischer, by merely adding acold concentrated solution of a metal nitrite to an alcoholic hydrogenchloride suspension or solution of the base, but when using thediarylamines with the same reactants, Wyler applied strictly anhydrousconditions in order to accomplish the conversion in a single step.

I have now found that the inherently difficultly convertiblediarylamines can be converted to the carbon nitroso derivatives in asingle step in a 2 much simpler manner and without the necessity ofusing difiicultly obtainable reactants, such as dry hydrogen chloride,absolute alcohol and dry sodium nitrite, if silicon tetrachloride (SiCh)is substituted for the hydrogen chloride. In this process I may usecommercial grades of alcohol such as the low molecular weight aliphaticalcohols which normally contain Water in percentages of from 1-5. Ifdesired, further amounts of water may be added and, of course, it is notnecessary to use dry reaction vessels. There is no loss in yield and, asa matter of fact, improved yields of carbon nitrosodiarylamines of goodquality are obtained. The process is carried out in its preferred mannerby introducing the silicon tetrachloride into a suspension of thediarylamine and an alkali metal nitrite in a commerical grade of analcohol, such as methanol, subsequently drowning the reaction mixture inan ice water mixture and finally isolating the carbon nitrosoarylamineby known methods most suitable to the specific amine employed. In somecases, the product may be filtered off as the hydrochloride followingthe drowning operation.

This process is not restricted to any particular secondary arylamines,but is of particular interest in the case of the diarylamines which aredifficultly convertible in a one-step operation to theC-nitrosodiarylamines. The process may be applied to any secondaryarylamine capable of undergoing the formation of N-nitroso derivativesand rearrangement to C-nitrosoarylamines. Typical examples of compoundswhich are capable of such rearrangement are: diphenylamine,phenyLa-naphthyIamine, di 1 naphthylamine, 3-acetylaminodiphenylamine,and 4- acetylaminodiphenylamine.

Although it is preferable to add the silicon tetrachloride to asuspension of the arylamine and alkali metal nitrite in an alcoholsolution, it is possible to first react the silicon tetrachloride withthe alcohol and add the arylamine to this mixture, after which thealkali metal nitrite may be incorporated. The amount of silicontetrachloride required to effect the conversion may vary, but for bestresults from 1 to 8 mols should be employed per mol of the base. Thetemperature at which the agent necessary for the nitrosation andrearrangement is added is preferably from 0 to 30 C.

The following example, in which the parts given are by weight unlessotherwise stated, will serve to further illustrate the invention, but isnot intended to limit its scope.

Example 169 g. of diphenylamine, equal to one gram mol, is dissolved in360 g. of methanol (commercial) by warming to 35-40 C. Thesolution iscooled to 5 C. and

80 g. of finely divided sodium nitrite is added. Over a period of 2-3hours 197 g. of silicon tetrachloride is added at 05 C. The mixture isthen stirred from 4-8 hours at 0-5 C., poured into 3000 cc. of icewater, stirred one hour, then filtered and washed with water orsaltsolution.

The l-nitrosodiphenylamine hydrochloride thus obtained can betransformed into the free base by dissolving it in alkali, filteringfrom any residue and precipitating the base with acetic acid. Thisproduct crystallized from a mixture of benzene and petrol ether has amelting point of 145- 146 C.

Having now described my invention and the best manner in which toperform it, what I-claim 1. The process of producing a C-nitrosodiarylamine which comprises reacting an alkali metal nitrite in analiphatic alcohol medium with an unsubstituted diarylamine in thepresence of silicon tetrachloride at a temperature not exceeding 30 C.while utilizing said silicon tetrachloride to react with the waterpresent to generate hydrogen chloride and maintain the reaction mixturein a substantially anhydrous condition.

2.- The process of producing a C-nitroso diarylamine which comprisesintroducing into an aliphatic alcohol media containing an alkali metalnitrite and an unsubstituted diarylamine, silicon tetrachloride at atemperature not exceeding 30 C. while utilizing said silicontetrachloride 'to react with the water present in the reaction mixtureto produce hydrogen chloride and maintain the reaction mixturesubstantially anhydrous, drowning the reaction mixture in an ice watermixture and isolating the C-nitroso diarylamine.

3. The process of producing a C-nitroso diarylamine which comprisesreacting at a temperature not exceeding 30 C. an unsubstituteddiarylamine and an alkali metal nitrite in methanol in the presence ofsilicon tetrachloride while utilizing the silicon tetrachloride to reactwith the water present to produce hydrogen chloride and maintain thereaction mixture substantially anhydrous, drowning the reaction mixturein an ice water mixture and isolating the resulting C- nitrosodiarylamine.

4. The process as defined in claim 1 wherein the aliphatic alcohol mediais commercial methanol.

5. The process of producing a C-nitroso diarylamine wh-ich comprisesintroducing silicon tetrachloride at a temperature not exceeding 30 G.

into a suspension of an unsubstituted diarylamine and analkali metalnitrite in commercial methanol while utilizing the silicon tetrachlorideto react with the water present to produce hydrogen chloride andmaintain the reaction mixture substantially anhydrous, drowning thereaction mixture in an ice water mixture and isolating the resultingC-nitroso diarylamine.

6. The process as defined in claim 1 wherein the unsubstituteddiarylamine is diphenylamine.

7. In the process of producing a C-nitrosor diarylamine by reacting at atemperature not exceeding 30 C. an unsubstituted diarylamine with analkali metal nitrite in an aliphatic alcohol in the presence of hydrogenchloride, the improvement which comprises generating the hydrogenchloride in the reaction mixture by the addition thereto of silicontetrachloride which operates to maintain the reaction mixture in asubstantially anhydrous condition.

STILES M. ROBERTS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS .Number Name Date 2,495,774 Roberts Jan. 31, 1950OTHER REFERENCES Parkes et al.: Mellors Modern Inorganic Chemistry,Longmans, Green & Co.,'New York, 'N. Y., new edition, 1939, p. 693.

1. THE PROCESS OF PRODUCING A C-NITROSO DIARYLAMINE WHICH COMPRISESREACTING AN ALKALI METAL NITRITE IN AN ALIPHATIC ALCOHOL MEDIUM WITH ANUNSUBSTITUTED DIARYLAMINE IN THE PRESENCE OF SILICON TETRACHLORIDE AT ATEMPERATURE NOT EXCEEDING 30*C. WHILE UTILIZING SAID SILICONTETRACHLORIDE TO REACT WITH THE WATER PRESENT TO GENERATE HYDROGENCHLORIDE AND MAINTAIN THE REACTION MIXTURE IN A SUBSTANTIALLY ANHYDROUSCONDITION.